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std::ctype

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Defined in header <locale>
template< class CharT >
class ctype;

Class ctype encapsulates character classification features. All stream input operations performed through std::basic_istream<charT> use the std::ctype<charT> of the locale imbued in the stream to identify whitespace characters for input tokenization. Stream output operations apply std::ctype<charT>::widen() to narrow-character arguments prior to output.

cpp/locale/ctype basecpp/locale/locale/facetstd-ctype-inheritance.svg
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Inheritance diagram

Two standalone (locale-independent) specializations are provided by the standard library:

Defined in header <locale>
std::ctype<char> provides narrow character equivalents of the minimal "C" locale classification. This specialization uses table lookup for character classification
std::ctype<wchar_t> provides wide character classification appropriate to the native character set

In addition, every locale object constructed in a C++ program implements its own (locale-specific) versions of these specializations.

Contents

[edit] Member types

Member type Definition
char_type CharT

[edit] Member functions

constructs a new ctype facet
(public member function)
destructs a ctype facet
(protected member function)
invokes do_is
(public member function) [edit]
invokes do_scan_is
(public member function) [edit]
invokes do_scan_not
(public member function) [edit]
invokes do_toupper
(public member function) [edit]
invokes do_tolower
(public member function) [edit]
invokes do_widen
(public member function) [edit]
invokes do_narrow
(public member function) [edit]

[edit] Member objects

static std::locale::id id
id of the locale
(public member object)

[edit] Protected member functions

[virtual]
classifies a character or a character sequence
(virtual protected member function) [edit]
[virtual]
locates the first character in a sequence that conforms to given classification
(virtual protected member function) [edit]
[virtual]
locates the first character in a sequence that fails given classification
(virtual protected member function) [edit]
[virtual]
converts a character or characters to uppercase
(virtual protected member function) [edit]
[virtual]
converts a character or characters to lowercase
(virtual protected member function) [edit]
[virtual]
converts a character or characters from char to charT
(virtual protected member function) [edit]
[virtual]
converts a character or characters from charT to char
(virtual protected member function) [edit]

Inherited from std::ctype_base

Member types

Type Definition
mask unspecified bitmask type (enumeration, integer type, or bitset)

Member constants

space
[static]
the value of mask identifying whitespace character classification
(public static member constant)
print
[static]
the value of mask identifying printable character classification
(public static member constant)
cntrl
[static]
the value of mask identifying control character classification
(public static member constant)
upper
[static]
the value of mask identifying uppercase character classification
(public static member constant)
lower
[static]
the value of mask identifying lowercase character classification
(public static member constant)
alpha
[static]
the value of mask identifying alphabetic character classification
(public static member constant)
digit
[static]
the value of mask identifying digit character classification
(public static member constant)
punct
[static]
the value of mask identifying punctuation character classification
(public static member constant)
xdigit
[static]
the value of mask identifying hexadecimal digit character classification
(public static member constant)
blank
[static] (C++11)
the value of mask identifying blank character classification
(public static member constant)
alnum
[static]
alpha | digit
(public static member constant)
graph
[static]
alnum | punct
(public static member constant)

[edit] Example

The following example demonstrates modification of a ctype other than ctype<char> to tokenize a CSV file

#include <iostream>
#include <locale>
#include <sstream>
 
struct csv_whitespace : std::ctype<wchar_t>
{
    bool do_is(mask m, char_type c) const
    {   
        if ((m & space) && c == L' ') {
            return false; // space will NOT be classified as whitespace
        }
        if ((m & space) && c == L',') {
            return true; // comma will be classified as whitespace
        }
        return ctype::do_is(m, c); // leave the rest to the parent class
    } 
};
 
int main()
{
    std::wstring in = L"Column 1,Column 2,Column 3\n123,456,789";
    std::wstring token;
 
    std::wcout << "default locale:\n";
    std::wistringstream s1(in);
    while (s1 >> token) {
        std::wcout << "  " << token << '\n';
    }
 
    std::wcout << "locale with modified ctype:\n";
    std::wistringstream s2(in);
    s2.imbue(std::locale(s2.getloc(), new csv_whitespace()));
    while (s2 >> token) {
        std::wcout << "  " << token<< '\n';
    }
}

Output:

default locale:
  Column
  1,Column
  2,Column
  3
  123,456,789
locale with modified ctype:
  Column 1
  Column 2
  Column 3
  123
  456
  789

[edit] See also

specialization of std::ctype for type char
(class template specialization)
defines character classification categories
(class template)
creates a ctype facet for the named locale
(class template)